GLACIAL FEATURES OF THE ALPS 5 



are determined by the laws which control the stir faces of moving 

 liquids, while the forms of the iVlpine valleys are governed by the 

 rules controlling the formation of the floors of moving liquids. Thus, 

 instead of the law of Playfair, the law of adjusted cross-sections 

 comes into action. 



There can be no doubt what particular moving liquid or quasi- 

 liquid is related to the features of the Alpine valleys, since it has been 

 recognized that all the greater Alpine lakes lie in the region of the 

 old glaciation, and later researches have proved this for all the special 

 features of Alpine valleys. The overdeepening, with all its accom- 

 panying features — the trough, the trough's end, and the lake lying 

 in it, with its shoulders and the hanging mouths of side valleys — 

 is confined to the area glaciated during the Great Ice Age, and the 

 moment you leave this area you reach the normal features of mature 

 valleys with accordant mouths of side streams; you reach mountains 

 whose summits are not dissected by corries. The concurrence of 

 Alpine valley troughs and old glaciers suggests the theory of origin 

 by glacial erosion. The theory of glacial erosion was advanced by 

 A. C. Ramsay for the formation of the Alpine lakes. We go a great 

 deal farther than he when we apply that theory to the formation of 

 the far more extended feature of the troughs in the Alpine valleys, 

 for the lake basins occupy only those parts of the troughs which 

 extend below the lowest parts of their circumferences. 



The erosive action of the glaciers has very often been denied, and 

 is even now denied by some, while it has been at various times vigor- 

 ously supported. This diversity of opinion is caused by the fact 

 that we cannot observe how actual glaciers act upon their bottoms, 

 their work being concealed by their icy mass. We usually see only 

 how the glaciers transport moraines and deposit them about their lower 

 ends. The fact that stone avalanches not rarely fall down from the 

 side walls of a valley on the surface of a glacier suggested the idea that 

 the material of the surface moraines is due entirely to the action of 

 weathering exercised on those cliffs which overlook the glacier. The 

 study of the moraines on actual glaciers, however, has revealed more 

 clearly the fact that they cannot be entirely derived from those cliffs, 

 but that they come in large part from the bottom of the glacier. 

 What effects are here produced by the glacier can be observed only 



